Various types of medical capsules have been widely used in the field, where the medical capsules are ingested into a human body for in vivo monitoring or examining purposes. For example, a medical capsule can be used to monitor the pH value of the gastrointestinal tract or temperature of different human organs. A medical capsule may also be used to deliver medicines to desired spots inside the human body or to collect samples, such as body fluids, inside a human body. Usually, the medical capsule includes a power source, such as batteries, so that the capsule can monitor/measure data, dispense medicine, or collect samples inside the human body without the need of external power. The power source along and other components of the medical capsule are enclosed inside a smooth housing adapted for easy swallowing. The power source and other components of the medical capsule are sealed in a housing. It is not easy to access the power source and other components of the medical capsule, after the medical capsule is manufactured, to enable or disable the power without special tools and/or skills. Furthermore, the medical capsule may not be administered soon after it is manufactured. Also, the medical capsule may have to be operational for extended hours during the course of travelling through the human tract; the power source is preferred to be disabled until right before it is administered into the human body. In other words, the power source to the medical capsule is enabled when the capsule is ready for administering into a patient's body. It is desirable to develop power-efficient, reliable and compact apparatus of power source control for medical capsules. The housing for the medical capsule may be fully sealed or watertight so that there is no direct access to any components inside the housing. Therefore, the power source has to be operated without opening the housing.